I don't have any specific ideas, but I would suggest you get your daughter's input. You might not agree with (or to) everything she suggests, but she'll thank you for it.

Agree with IdaClaire. Also, what's working and what's not working for her in this room? Is it simply the need to get a bigger desk? What's the budget? Does she have inspiration pics?

A cork wall so she can pin posters and pictures to her hearts delight (and mom and dad can paint it or stencil a pattern on it so it doesn’t scream I’m a big cork wall)

she has final say on everything! I am not driving the project. But yes she wants a bigger desk and she is changing the colors of the walls.

and the question for us here is... ??

luis, you'll have to give us something to go on, otherwise we could post 500 pictures.

she wants a bigger desk. Ok,,,like, what kind of desk? ask her for a picture.

does she want the desk to double as a vanity?

what color does she want the walls?

what kind of style does she like?

art?

bedding? colors? flowers? stripes?

ask her to show you a picture of a bedroom she really likes, then post that pic here

She's 15. She knows what she wants, ask her.

show her some of these

I'm digging this black Stikwood in a herringbone behind the white bed, white walls, black/gray rug, white drapes and a cool light.

or maybe she wants dark/moody walls and all white bedding

every teenage girl likes fairy lights.

Or Curtain LED lights

this is a white desk that doubles as a vanity:

check ikea for a long desk/storage item like this one.

You could do this under the double windows and move the bed to the right more. or do it on the other wall. plenty of room for homework, and the cabs offer more storage.

another ikea desk w/shelving

Or one like this. bookcase for all sorts of storage, large desk (Ikea) with drawers, plenty of room for schoolwork,,,and it looks really cool. (if she's into the black and white) if not, substitute gold or silver or whatever color she likes)

maybe she wants a removable wallpaper mural on the ceiling. easy enough to do.

Pink/white desk area. notice the extra shelving and feminine decor items.

You said she wants a bigger desk, you need more information from her about what she wants to do on the desk and store there.

Does she need space for filing? Will she be drawing or drafting?

Does she need space to put a laptop or does she have a regular computer monitor and screen? Two screens? Does she have a printer too? Other computer paraphernalia?

How many feet of bookshelves does she need?

Approximately how many feet of drawer space does she need for inside the desk?

Will it be for general office supplies, or does she have art supplies too?

Approximately how many feet of drawer space does she need for clothing?

Does she study and do homework in her bedroom or somewhere else in the house?

Does she have friends sleep over so that you really need place for two to sleep in that room?

How old is she, what grade is she in, and when she starts college, do you think she will stay living with you, or do you think she will go away?

Of course one never can predict the future, but I ask to get an idea how much $$ you might want to sink into this.

Firstly I want to tell you that it is marvelous that you are thinking about re-decorating to suit your teenage daughter's preferences and needs.

Back to the subject at hand.

Bed

They often have sleepovers. I have found (and I had one myself) that trundle beds work very well for this (unless you are fortunate enough to have a guest room. I prefer the type of trundle bed where the extra bed is underneath and rolls out on wheels and pops up so the two beds are on the same level. I especially like it when instead of sticking out from the wall, the long axis of the bed is against the wall. You can get the bed with a wooden or metal daybed type upper portion against which to put large comfy thick dense pillows, and it becomes a "sofa" for your daughter and her friend. Even without that frame, you can purchase or have made two large pillows each 1/2 the length of the bed of thick dense foam covered in batting, then muslin, and then a zippered cover of whatever fabric you choose. Get two sets, and make them machine washable!

Desk

For serious work, especially with a computer, often an L shaped configuration works well, and this is best done in the corner of a room. Even if your daughter works with a laptop almost all the time, she will appreciate a hookup to a second screen at home as that will facilitate report writing.

She can have source material on the second screen while she does the writing on her word program on the first screen.

It's also just nice to compare two different things at the same time on nice size screens, instead of a split screen image which is small.

And sometimes the second screen is best at an angle. from the first screen.

Normal desk height is 30 inches.

If the windows come down a bit low, you might be able to remove the lower parts of the window (the stool and apron) without affecting the function of the window to allow placement of a desk length.

If she is an artist she may need an easel. Or depending on the type of art, she may prefer a drafting table. She may want the type of storage table with many shallow drawers for art supplies. She may want something like that for all her cosmetics and jewelry! There are inexpensive versions of those as well, and you can get one or two of those to tuck under one of the arms of the L.

Storage

To use space most efficiently, think vertically!

In the space between the windows you can put up shelves, or even mount a properly sized bookshelf, so no space is wasted by the triangular brackets.

Above the desk there are so many different ways to store things, systems you can make or buy.

Look at the IKEA kitchen wall storage units that have attractive bins and baskets that hang from rods. Only instead of using them for kitchen utensils, your daughter can use them for pens and pencils, rulers, staplers, tapes, paint brushes, etc. You can make something yourself out of peg board. There are a myriad of ideas on the internet.

Look up do it yourself (DIY) home office ideas, and DIY home office storage.

Decor

Of course consider your daughter's preferences. I would try to encourage neutrals (such as shades of white) for the large things and use her favored colors for the smaller things, as her tastes may change.

A 12 year old may love pink, and by the time she is 14 she may despise it and want orange and by the time she is 15 she may want black!

The other advantage of white is that it is washable and often bleachable.

The other advantage of light walls is that she can put up any type of poster or wall decor. There are non-stick wall decals that are lots of fun, too, not in the least childish either, and some marvelous easy to put up and take down wallpaper that won't ruin your walls.

Good luck!

aluislugo, as you can see, ideas aren't rare when it comes to teenagers' rooms! :) My suggestion to you and your teen is to plan the room redo by drawing out the room dimensions on graph paper. Mark the windows, outlets, doors and any other particularity of the space. Then you can try out different furniture layouts with paper cutouts of furniture pieces. Much easier than moving actual furniture. :) Start with the bed placement. Then add the larger desk she needs. See if there's enough room to move around. Add the bedside table. Decide on clothes storage and add whatever pieces are necessary for that. Once the furniture layout is decided, she(?) can shop for the furniture, bedding and decor. Hope this helps. Please keep us posted. I'd love to see her room in progress and once done. Teen rooms are so much fun to do!

I went to houzz hunt and described the room and here are many results that have green and lavender. https://www.houzz.com/photos/query/teenage-girls-bedroom,-she-wants-lavender-and-green/nqrwns

I asked my daughter for a theme and that gave a direction for color and decor. clear out everything but what you are keeping. need a clean slate. my daughter did bohemian so we put matresses on floor and used footboard as headboard and stored headboard. went to goodwill for decor and lamp. not my style but she loved it. now my son wanted industrial so we did a dark grey wall with grey red white bedding. again again, not my style but he loved it.